1. Field of the Invention
The present invention relates to a control device for controlling the switching of a switching element of a power conversion device, and more particularly, to a power conversion device control device and a power conversion device control method, which control the switching of a switching element by pulse width modulation (PWM).
2. Description of the Related Art
When the switching on/off of a switching element of a power conversion device is controlled with a constant switching frequency, electrical noise of high noise level is generated in some cases due to the switching frequency. The electrical noise generated by the power conversion device can harm other electronic devices by causing malfunction, breakdown, and the like. In addition, if the switching frequency used to control the switching of the switching element is in the auditory range of humans (specifically, a frequency range of 20 Hz to 20,000 Hz), electromagnetic noise due to the switching frequency can cause auditory noise.
Arranging a snubber circuit, a noise filter, or other noise countermeasure parts on the power conversion device in order to control the electrical noise results inevitably in an increase in cost and device size. Therefore, there has hitherto been proposed a technology of lowering the peak value of electrical noise generated by a power conversion device by diffusing the electrical noise, without arranging noise countermeasure parts thereon.
Specifically, the switching frequency for controlling the switching of switching elements that are arranged in half-bridge circuits of respective phases in a power conversion device is varied from one half-bridge circuit to another (see, for example, Japanese Patent Application Laid-open No. 2013-219916). Another way is to set the same switching frequency to control switching elements that are arranged in half-bridge circuits of the respective phases in a power conversion device, and to switch the switching frequency with time from one frequency out of a plurality of switching frequency levels to another frequency sequentially (see, for example, Japanese Patent Application Laid-open No. 2012-165486).
However, the related art has the following problems.
In the related art of Japanese Patent Application Laid-open No. 2013-219916, where the switching frequency varies from the half-bridge circuit of one phase to the half-bridge circuit of another, electrical noise generated by one half-bridge circuit is not superimposed on electrical noise generated by another half-bridge circuit. Although this brings about an effect in that the electrical noise is diffused more than when the switching frequency is constant, the peak value of the electrical noise generated by each half-bridge circuit is still high. The resultant problem is a chance of electromagnetic noise being generated due to the switching frequency, as well as a chance for harm to other electronic devices.
In the related art of Japanese Patent Application Laid-open No. 2012-165486, electrical noise generated by the power conversion device increases in proportion to the number of half-bridge circuits that are arranged in the power conversion device. This means that the related art of Japanese Patent Application Laid-open No. 2012-165486 applied to a multi-phase inverter is lower in electrical noise diffusing effect when the number of half-bridge circuits included in the multi-phase inverter is higher. The resultant problem is a chance of electromagnetic noise being generated due to the switching frequency, as well as a chance for harm to other electronic devices.